In the following of the document, a unit designates a set of interdependent and non-separable vehicles.
Each unit of a train includes a module capable of ensuring that the different functions relating to the safety of the train are fulfilled, such as for example the calculation of the speed of the train, the handling of the opening of the doors or further emergency breaking. Another primary function which also relates to the safety of the train, consists of being able to determine the configuration of the train, in other words the order according to which the units are connected to each other. Fulfillment of this function allows the train to know its length, the knowledge of this parameter being essential during the crossing of reversal switches, or further know the mass distribution of its units, which is notably useful for parameterization of the features of the train.
This determination of the configuration of the train is achieved before starting the train, when it is at a standstill, and is conventionally carried out by safety equipment installed on the ground, and able to determine the relative position of the units. Such pieces of safety equipment for example include radio transmitters, track sensors and/or circuits, operating autonomously or as a combination with each other. These pieces of equipment then transmit the configuration of the train to the train itself, the train then checks its configuration by reading coupling electric couplers installed between each unit, and able to determine, for each unit of the train, the presence or the absence of an adjacent unit.